Several major natural disasters, such as earthquakes, hurricanes or tsunami, have occurred in the last decades causing a large number of victims and a considerable monetary loss through the collapse of bridges, buildings, energy infrastructures, or transportation systems. Therefore, the needs to identify structural damage and to monitor its evolution impose the development of structural health monitoring (SHM) detection techniques. The main objective of the SHM research is to develop methods for observing in-situ structural behavior under different loading conditions during predetermined time periods or over the structure lifetime and to detect the deterioration of structural or material properties.
A wide range of sensors have been developed particularly for generating and receiving acousto-ultrasonic waves, exemplified by piezoelectric wafer active sensors (PWAS) and fiber Bragg grating (FBG) sensors. Both are effectively used in acousto-ultrasonic based damage identification because a single technology is not suited for the entire range of applications. FIG. 1 illustrates the set-up of the hybrid acousto-ultrasonic concept. Surface bonding or embedding are two ways of integrating the PWAS or FBG into a host structure. In the case of embedded, the mechanical behavior of the composite laminate are not degraded by the presence of the FBG or PWAS inclusion.
As such, it would be desirable to provide integrated miniaturize transducers that can be permanently bonded to the structure and left in place to be activated on demand and demonstrate that they can be used to monitor structural integrity in service conditions with high reliability & durability. It would also be desirable to develop a combined piezo-optical sensing system and to prove high reliability over the structure lifetime, since unjustified maintenance actions are quite costly to the operator.